2011 年 26 巻 4 号 p. 326-331
This study focused on modification effects of soot-containing particles by aging and in-cloud scavenging processes. Morphological features and mixing states with water-soluble materials of soot-containing particles collected at two observation sites were analyzed by a transmission electron microscopy (TEM) with extraction of water-soluble materials. To elucidate the aging effects after their transport from megacities, we obtained aerosol samples for continental outflow at Cape Hedo, Okinawa in March 2008. Most soot-containing particles (0.2-0.7 μm) were mixed with water-soluble materials. Some soot-containing particles were found as clustered particles in multiple small (ca. 0.3 μm) spheroids. They were attributed to coagulation of solid spheroidal particles. At Mt. Tateyama (2300 m a.s.l.) in June 2007, cloud interstitial particles were measured using fog (>10 μm)-cut inlets. During fog condition under high precipitation (2-6 mm/hr), most of cloud interstitial particles (0.3-0.5 μm) were less- or non-hygroscopic particles. The results of TEM analysis suggested that most of the cloud interstitial particles were soot particles without water-soluble materials. These observation results suggested that morphological modification with coagulation process under high aerosol concentration and population change of the particles with in-cloud scavenging process are key processes controlling morphology and mixing states of soot-containing particles in the atmosphere. These changes of soot-containing particles must be considered when estimating direct radiation effect of aerosols from megacities and assessing climatic effects by long range transport of soot aerosols.